Ignition system



Jun 5, 1 1 R. J. DAVIS 2,555,922

IGNITION SYSTEM Filed March 3, 1950 l6 30 /a /Z4 3 nnentor 1 9055127- uf Dav/s (Ittorncgs Patented June 5, 1951 UNITED STATES PATENT OFFICE IGNITIQN SYSTEM Robert J. Davis, Taft, Kern County, Calif. Application March a, 1950, Serial No. 147,413

1 Claim. 1

This invention relates to improvements in ignition systems and has for its essential object the provision of an ignition system in which the duration of the spark discharge is shorter than that hitherto obtained in conventional ignition systems, with consequent lengthening of the normal life period of spark plugs utilized in the improved system.

In summary, the invention comprises the introduction of a condenser into the secondary side of a magneto ignition system, with the condenser having a suflicient capacitance value to effect a change in the normal frequency of oscillation of the magneto circuit and thereby reduce the duration of the discharge across the spark gap. This spark period reducing function may be made more pronounced if, in addition to the incorporation of the condenser into the magneto circuit, an inductance and resistor circuit is connected into the secondary side of the magneto circuit across the condenser.

Further details and advantages of the invention will be apparent from the following description taken in conjunction with the drawing forming part of this specification and comprising Figure l, which is a schematic representation of a magneto ignition system embodying the improvements of the invention, with the ignition system being shown for purposes of simplicity as containing a single spark gap.

Referring to Figure 1 for further details of the invention, the ignition system, which by way of example is shown as being of the magneto type, includes the following conventional elements: A primary circuit comprising a core l0, and inductance coil I2 wound thereon, a condenser l4, and points [6 and 18 adapted to be sequentially engaged and disengaged in timed sequence by some conventional means, such as a cam, not shown; a secondary circuit comprising an inductance coil 20 wound on the core [0, a ground connection 22 for said coil, a spark gap 24, and a ground connection 26 for the spark gap lead.

This conventional system is modified by the inclusion in the system between the inductance coil 20 of the secondary circuit and the spark gap 24 of a condenser 28. The capacitance value of the condenser 28 is selected in accordance with the particular values of the elements of the balance of the magneto ignition system. For example, when a conventional high tension magneto, such as that designated as MJA-4C-106 American Bosch, was used, the condenser 28 was provided with a capacitance of 0.0075 microfarad.

The values for the elements comprising the magneto circuit for the designated American Bosch unit are as follows: An inductance of 0.00013 henry for the coil I2; an inductance of 2.16 henries for the coil 20; and a capacitance of 0.25 microfarad for the condenser 14. The dimension of the spark gap 24 is a variable quantity within the range of approximately 0.022 to 0.040 inch. Where a given induced voltage in the sec-' ondary circuit of the magneto system is concerned, the minimum distance across the gap enabling the voltage to jump the gap will vary in accordance with conditions of.temperature and gas pressure at the spark gap.

I have also used the magneto designated as MJA-4C-1l3 heavy duty American Bosch in the modified ignition system of the invention, in which case the capacitance value for the condenser 28 was 0.00375 microfarad. The respective values for the elements I2, l4 and 20 comprising the magneto circuit of the MJA-4C-1ll3 magneto are as follows: An inductance of 0.00013 henry; a capacitance of 0.50 microfarad; and an inductance of 2.16 henries.

The current source for the illustrated example of the modified ignition system is the magnet of the magneto which, upon rotation, induces a current by electro-magnetic induction in the primary coil l2. When the points or contacts l6 and [8 are open, the primary current flowing between the coil l2 and the points It and i8 breaks down, resulting in an oscillatory discharge by the condenser 14 and the coil [2. This discharge is mutually induced and magnified in the secondary coil 20, but the normal frequency of oscillation at the secondary side of the magneto circuit is believed to be so varied by the condenser 28 that the resultant frequency of the secondary side is out of tune with the frequency of the primary side of the magneto circuit, and thus when the induced voltage in the secondary side of the circuit becomes sufiiciently high to jump the spark gap 24, the duration of the spark is reduced over what it would normally be in the absence of the condenser 28, thus reducing wear at the points of the spark plug.

I have also found that somewhat better results are produced insofar as spark period reduction is concerned if in addition to the condenser 20 the secondary side of the magneto circuit is provided with a circuit comprising an inductance coil 30 and a resistor 32 in shunt relation to the condenser 28. When the MJA-4C-106 American Bosch magneto, having values for its respective elements as above set forth, was used, the condenser 28 had the same capacitance value of 0.0075 microfarad, while the elements 30 and 32 were provided with values, respectively, of an inductance corresponding to 21 turns based on a one-half inch diameter and a resistance of one megohm. When the MJA-4C-113 heavy duty American Bosch magneto, having the respective values for its elements as above set forth, was used, the capacitance value for the condenser 28 was maintained at 0.00375 microfarad, while the values for the coil 30 and resistor 32 were, respectively, 0.00013 henry and a resistance of 2 megohms. 7

What I claim as new and desire to secure by Letters Patent is:

An ignition system comprising a primary side having an induction coil and a condenser, a sec- ROBERT J. DAVIS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 7 Date ' Number Name 2,131,018 Scott Sept. 20, 1938 2,280,426 Scott Apr. 21, 1942 

